An adjective used to describe a foolish or stupid person. It may sometimes be used in a serious context but is generally utilized as a playful insult. It is aslo a "politically correct" way of calling someone a "retard". The word came into useage by way of a lyric in an Ian Erix song and is reportedly an acronym for Un-Non-Tard ("Tard" having been derived from the word "Retard").

Oh my G-d, you've never heard of urbandictionary.com??? You are such an unt!!!

She's the biggest unt...she would lose her head if it wasn't attached to her shoulders!

A short grunt-like shout directed at someone (usually from a distance) who has very recently done something embarrassing. ie: Tripping over.

Bill: Jamie's quite good at basketball, isn't he?
Fred: Yeah, he is pretty good, wish i had that skill. I really admire him.
(Jamie trips over while trying to take the ball from someone)
Fred and Bill in unison: Unt!